We prove that if a finite alphabet of actions contains at least two elements, then the equational theory for the process algebra BCCSP modulo any semantics no coarser than readiness equivalence and no finer than possible worlds equivalence does not have a finite basis. This semantic range includes ready trace equivalence.

This paper discusses the role of existence presuppositions and conceivability in linguistic interpretation. In particular, it is discussed evidence that the non-emptiness requirement on universally-quantified propositions might be satisfied through access to a background of knowledge concerning what might be the case in the actual world, as opposed to a background of knowledge concerning what i...

Many computational models of narrative include representations of possible worlds—events that never actually occur in the story but that are planned or perceived by the story’s characters. Psychological tools such as QUEST are often used to validate computational models of narrative, but they only represent events which are explicitly narrated in the story. In this paper, we demonstrate that au...

Interval Temporal Logics over infinite intervals are studied. First, the ordinary possible worlds models are extended to infinite possible world models. Accordingly, an axiomatic system is proposed and it has been proved complete. Secondly, infinite intervals are included in a logic over abstract intervals. A corresponding axiomatic system is given and proven to be complete also.

A. The most popular theory of how to evaluate counterfactuals is to use the LewisStalnaker logic together with some reasonably tractable refinement of our ordinary notions of similarity. This approach is misguided because for some ordinary counterfactuals, irrelevant possible worlds end up determining the counterfactuals’ truth values. This undermines some of the support for the Lewis-St...

I briefly discussed a view (see (Lewis, 1986)) which attempts to use (SC) to provide a theory of possible worlds aimed at using (SC) to reduce modality. This review sets aside such reductive theories of possible worlds, and concentrates instead on four leading nonreductive theories. Though some of these theories have reductive variants, the versions that figure most prominently in contemporary ...

In this paper, we study the semantics for the logics of preference based on possibility theory. Possibility distributions representing the preference between worlds are associated with the possible world models for dynamic logics. Then the preference between actions are determined by comparing some measures of their consequences. We will define different logics of preference by considering the ...

In ’Quiddistic Knowledge’ (Schaffer [2005]), Jonathan Schaffer argued influentially against the view that the laws of nature are metaphysically necessary. In this reply I aim to show how a coherent and well-motivated form of necessitarianism can withstand his critique. Modal necessitarianism -the view that the actual laws are the laws of all possible worlds -can do justice to some intuitive mot...

Just as set theory can be divorced from Ernst Zermelo’s original axiomatization of it, counterpart theory can be divorced from the eight postulates that were originally stipulated by David Lewis (1968, p. 114) to constitute it. These were postulates governing some of the properties and relations holding among possible worlds and their inhabitants. In particular, counterpart theory can be divorc...

A unifying semantic framework for different reasoning approaches provides an ideal tool to compare these competing alternatives. A historic example is Kripke’s possible world semantics that provided a unifying framework for different systems of modal logic. More recently, Shoham’s work on preferential semantics similarly provided a much needed framework to uniformly represent and compare a vari...